The cloning of frogs from somatic cells demonstrated that differentiation from the zygote into specialized cell types was a reversible process. The transplantation of somatic nuclei into unfertilized mammalian oocytes resulted in the cloning of sheep, mice, cows and various other mammalian species.
The derivation of embryonic stem cells from human blastocysts brought the prospect of combining nuclear transfer and stem cell derivation to generate cells and tissues for patients requiring replacement of diseased cells or tissue. This concept was realized in the mouse for the correction of immunodeficiency and of Parkinson's disease (Rideout et al. 2002 Cell 109(1): 17-27). Nuclear transfer stem cells were also derived from the rhesus monkey (Byrne et al., 2007 Nature 450 (7169): 497-502). However, most previous attempts at human somatic cell nuclear transfer (SCNT) using human cells have resulted in the generation of nuclear transfer embryos that consistently arrest at the late cleavage stages with karyotypic and transcriptional defects, prohibiting further development or stem cell derivation. Prior to the present invention, the only SCNT methods that were shown to be effective in generating human blastocyst stage embryos and stem cells derived therefrom were those that involved transferring a diploid human somatic cell genome into a haploid human oocyte without removing the oocyte's genome. (See Noggle et al. 2011. Human oocytes reprogram somatic cells to a pluripotent state. Nature 478(7367): 70-75. See also, U.S. Patent Application Pub. No.: US 2012/0129620). Such methods resulted in the generation of embyros and stem cells that were triploid. Thus, prior to the present invention there remained a need in the art for a method of generating a diploid human nuclear transfer embryo capable of developing to the blastocyst stage and from which diploid human pluripotent stem cells could be derived.